Heavy oil and bitumen are expected to become increasingly important sources of fuel in the coming decades. SAGD is a commercially viable and widely used recovery technique for heavy oil and bitumen. However, it remains an expensive technique and requires large energy input in the form of steam. Energy intensity of SAGD, environmental concerns and the threat of a carbon tax make it imperative to find new oil extraction technologies. Co-injecting a hydrocarbon additive with steam offers the potential of higher oil rates and recoveries with lower energy and water consumption.
A reservoir simulation study using a 20?12?15 3D Cartesian model and Athabasca fluid and reservoir properties was conducted to evaluate this hybrid process. The role of hydrocarbon additive in the steam chamber and its effect on the performance of SAGD was investigated.
Simulation results revealed the parameters that will have the greatest impact on the process performance and determined the effectiveness of each hydrocarbon additive in improving the performance of SAGD. The results also showed that selecting the most suitable hydrocarbon additive depends on the operating condition as well as the original reservoir fluid composition.
Over 90% of the world's heavy oil and bitumen trapped in sandstones and carbonates are deposited in Canada and Venezuela. There are extensive deposits in Alberta that can be the principal source of fuel in the coming century. The Athabasca Oil Sands, the largest petroleum accumulation in the world, are deposits of heavy oil and bitumen which mostly occur at depths that are suitable for in-situ bitumen extraction. At original condition, the viscosity of Athabasca bitumen is over one million centipoises. The key parameter to produce this bitumen is to lower its viscosity and mobilize it to the production well. There are two main techniques for the reduction of bitumen viscosity: first is to increase heavy oil temperature, and second is to dilute the viscous bitumen by lighter hydrocarbon solvents.
The Steam Assisted Gravity Drainage1 (SAGD) process was developed to recover heavy oil and bitumen by draining the heated oil from around the growing steam chamber, driven by gravity, to the production well2. In this method, steam is injected into the reservoir via a horizontal well. Injected steam forms a steam chamber in the depleted area of the reservoir and this steam chamber grows upward and laterally as the process advances. At the edge of steam chamber, bitumen has extended contact with steam, where steam releases its latent heat to the bitumen and increases its temperature. Further, at the edges of the steam chamber, heated oil and steam condensate drain, forced by gravity, to the horizontal production well, positioned 5 m to 10 m below and parallel to the injection well. Figure 1 displays a cross section of the steam chamber and injection and production well. This method is taking advantage of temperature for lowering the viscosity of heavy oil. Figure 2 shows the effect of temperature on the viscosity of Athabasca bitumen which was plotted by using Mehrotra and Svrcek3 correlation, Equation 1.
